The closest prior art known to us is the material contained in U.S. Pat. No. 4,140,469 issued Feb. 20, 1979 for "Apparatus for Forming Ceramic Bodies." This patent issued to Robert R. Baker, one of the inventors set forth herein.
U.S. Pat. No. 4,140,469 discloses an apparatus designed for bonding a ceramic body to an interior annular surface of a ring-shaped body formed of ceramic material. The apparatus disclosed includes a blade ring 10 encapsulated by an encapsulating medium 20, with the exception of an inwardly facing bonding surface 16 of the blade ring. The encapsulated blade ring is held in the apparatus by means of a restraining sleeve 38 of ring shape. The patent indicated that this restraining sleeve 38 has an inner diameter equal to the diameter of the inwardly facing bonding surface 16 of the encapsulated blade ring 10. The disclosed structure also includes a die member 56 which has a diameter slightly less than the inside diameter of the restraining sleeve 38 so that the die member is movable therein.
As disclosed in U.S. Pat. No. 4,140,469, the die member 56 is moved downwardly within the restraining sleeve 38 so that silicon nitride powder 66 contained within a volume 64 is compacted in order to form a hub element 18, and simultaneously with the formation of that element, to achieve a bonding of that element to the inwardly facing bonding surface 16 of the blade ring 10.
The purpose of the method of the present invention is to achieve the best bond possible and also to minimize any distortion and/or cracking of the outer ceramic body, in the particular case described herein, the blade ring 10, when forming of the inner ceramic body 18 which is not only formed, but also simultaneously bonded to an inwardly facing surface 16 of the outer body. The exact manner in which the improvement in the method is achieved will be set forth in greater detail in the remaining portion of this specification.